There are already known various constructions of fuel cells, among them such using a quantity of acid electrolyte and such employing a proton exchange membrane (hereinafter collectively referred to as "electric charge transfer body" for the sake of simplicity) confined between respective cathode and anode electrode plates. The general principles of construction and operation of such fuel cells are so well known that they need not be discussed here in any detail. Suffice it to say that a gaseous fuel and an oxidizing gas are supplied to the anode electrode plate and to the cathode electrode plate, respectively, and distributed as uniformly as possible over the active surfaces of the respective electrode plates (that is, the electrode plate surfaces that face the electric charge transfer body and each of which is usually provided with a layer of a catalyst), and that an electrochemical reaction takes place at and between such electrode plates, with attendant formation of a product of the reaction between the fuel and oxygen, release of thermal energy, creation of an electrical potential difference between the electrode plates, and travel of electric charge carriers between the electrode plates, wherein the thus generated electric power usually constitutes the useful output of the fuel cell.
The fuel cells of the type here consideration, regardless of the kind of the electric charge transfer body being used therein, have one thing in common, namely, the fact that at least the electrode plates used therein are porous. In acid fuel cells, such porosity is needed primarily to supply and distribute the respective gaseous media, which are fed to the areas of the cathode and anode electrode plates that face away from the acid electrolyte body, to the respective active surfaces, but often also to store some replenishment electrolyte and/or to provide for removal of the reaction product from one or the other of the active surfaces. On the other hand, in proton exchange fuel cells, where the gaseous media can be supplied directly to the active surfaces, the porosity is still needed for the reaction product (water) removal.
It will be appreciated that, when porous elements such as the aforementioned electrode plates are used in fuel cells, it is necessary to assure that neither any liquid, such as liquid electrolyte, nor any of the gaseous media, be able to flow out of the periphery of the respective porous element. In this respect, the possibility of the gaseous media escaping through or even reaching the periphery of the respective porous element is a more serious one of the conditions to be prevented, not only because such escape would result in a loss of a portion of the respective supplied gaseous medium with attendant reduction in the operating efficiency of the fuel cell, but also, and possibly more importantly, because the mixture of the gaseous fuel with the oxidizing gas or with ambient air could create a safety concern.
In recognition of this situation, it was already proposed, for instance in the U.S. Pat. No. 4,555,324 to Ueno et al, to externally coat each of at least some of the edge portions of fuel cell electrode plates with a layer of polytetrafluoroethylene or a similar substance that, at least in theory, prevents both liquids and gases from passing therethrough and thus from reaching the outer periphery of the thus coated electrode plate edge portion. However, experience has shown that, as advantageous as this approach may seem at the first glance, serious problems are encountered when it is attempted to implement this approach in practice, especially as far as the structural integrity and gas impermeability of the thus coated edge portion is concerned.
Another solution to this problem is disclosed, for example, in the U.S. Pat. No. 4,652,502 to Breault et al. This solution is based on the recognition of the fact that no serious detriment is encountered when a liquid, such as liquid electrolyte, is permitted to reach the periphery of the respective electrode plate, so long as it is assured that this liquid is prevented by capillary forces from actually flowing out through such periphery. Based on this recognition, it is disclosed there that the edge regions of the electrode plates are densified by the introduction into the pores of such regions an impregnating liquid substance which, after curing or similar treatment, leaves behind a residue that only partially fills the pores but permits the aforementioned liquid to penetrate into and fill the remainder of such reduced-size pores, thus forming a so-called wet seal. This wet seal and the surface tension or capillary forces associated therewith then prevent any gaseous medium from penetrating from the interior to the exterior of the respective electrode element. Even here, however, the results are less than satisfactory, if for no other reason then because the liquid electrolyte or other liquid constituting the wet seal is able to reach the outer periphery of the fuel cell and, for instance, evaporate therefrom or cause other deleterious consequences.
Such problems are avoided by adopting an approach such as that disclosed, for instance, in the U.S. Pat. No. 4,640,876 to Warzawski et al where the plate-shaped porous electrode element is mounted in or on or supported by a solid frame which is separate and distinct from the electrode element but which is contiguous to the electrode element and completely circumferentially surrounds the same, thus in effect forming a plate-shaped fuel cell component therewith. Inasmuch as the frame, being solid, is impermeable to both liquids and gases, and because any interfaces between the frame and the plate surrounded thereby and/or between the adjacent frames juxtaposed with one another in a stack, can be sealed, the possibility of escape of any fluid, be it gas or liquid, to the periphery of the aforementioned plate-shaped fuel cell component can be avoided.
However, an arrangement like this also suffers of several disadvantages which, albeit different from those discussed above, detract from the technical and/or commercial feasibility of this approach. So, for instance, the very existence of the interfaces between the frame and the plate-shaped element, with attendant need for sealing such interfaces to prevent internal gas and/or liquid flow, adds to the complexity of the arrangement. Moreover, the periphery of the plate-shaped porous element is received in a recess of the frame so that shear stresses can occur at this location.
Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a plate-shaped fuel cell component which does not possess the disadvantages of the known components of this kind.
Still another object of the present invention is so to develop the component of the type here under consideration as to minimize the internal stresses therein.
It is yet another object of the present invention to design the component of the above type in such a manner as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.
A concomitant object of the present invention is to devise a method of making the component of the above kind which is easy to perform.